Painting an old aluminum trailer

I have responded to an ad in craiglist for a travel trailer that the owners want repainted. I am an artist and they want something "different". They are not planning on compensating me for my time, that was in the ad. The payback for me is the rolling advertisement.

I know I have to clean but do I have to prime? I have been reading various blogs for an hour and am not sure. for the design itself I am planning on doing larger areas with a mask and spray technique. But I would like to do details with other media, including brushed on paint, and possibly colored pencil, and sharpies.

I know this is going to take a long time. And yes I am probably a little crazy. But I would like some suggestions on how to approach this if anyone has ever painted an old travel trailer, or knows someone who has done an art piece of this magnitude. I have not met with the owner yet, but want a little bit of info before I do.